1. Field of the Invention
The invention relates to a battery-powered power tool which drives a motor by a battery.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2006-175592 discloses a battery-powered electric hammer drill having a battery for driving a motor. According to this known art, the motor powered by the battery and a mechanical arrangement are housed within a tool body in the form of a housing. The mechanical arrangement including a motion converting mechanism for linearly moving the hammer bit in its axial direction and a power transmitting mechanism for rotating the hammer bit around its axis serves to drive a hammer bit by rotative power transmitted from the motor. The motor is disposed such that its axis of rotation extends in a direction transverse to the axial direction or a direction of movement of a tool bit in the form of the hammer bit. Further, a handgrip designed to be held by a user is disposed rearward of a tool body on the tool body opposite from the hammer bit and extends in a direction transverse to the axial direction of the hammer bit. A battery is mounted to an extending end or a lower end of the handgrip rearward of the motor.
A power tool such as a hammer drill is used in various manners, including the manner of performing an operation in a horizontal position by pointing the hammer bit upon a vertical wall, the manner of performing an operation in an upward orientation by pointing the hammer bit upon a ceiling, and the manner of performing an operation in a downward orientation by pointing the hammer bit upon a floor. Therefore, in order to alleviate the user's fatigue, it is important to enhance the usability (ease of use) in use of the power tool. Particularly, in the case of the hammer drill in which the user holds the handgrip and performs an operation, while applying a forward pressing force and pressing the hammer bit against a workpiece, the greater the vibration in the striking direction of the hammer bit during operation (the longitudinal moment around a center of gravity), the greater the burden upon the user. The magnitude of this moment depends on the position of the center of gravity of the power tool. Specifically, the moment becomes greater as the position of the center of gravity is brought farther away from the axis of the hammer bit.